The purpose of this NCRR Shared Instrument Grant application is to secure funding to purchase an ImageStreamX imaging flow cytometer for the Flow Cytometry Core Facility (FCCF) at the University of Virginia School of Medicine. The FCCF is a very heavily used core facility at the University of Virginia and provides flow cytometry related services on a fee for service basis to the University community in general and particularly to NIH funded investigators in the School of Medicine. The FCCF currently serves over 200 investigators from the laboratories of 95 PIs in 27 different departments. The FCCF purchased the first generation ImageStream100 in 2005 with funds from the School of Medicine and contributions from individual investigators, departments and centers within the SOM. This technology was quickly adopted by a number of investigators that led to several key publications early on. The University of Virginia has become well known as a leader in the use of this technology and has had 19 publications employing the technology, three of which have been featured on the cover of major Journals. The number of investigators utilizing this technology has continued to grow with currently 18 PIs using this technology in their research. Some of the common applications for which the instrument has been used have been studies of apoptosis, yeast cell cycle, protein translocation, protein colocalization, shape change assays, T cell-APC conjugate analysis, trogocytosis, phagocytosis, rare cell identification, viral load/replication, studies of cell cycle/mitosis, and morphological and phenotypical identification of functional immune cells. In many of these applications, studies have been compromised by the limitations of the current instrumentation, including the limited number of colors (markers) that can be simultaneously evaluated, slow acquisition rates, lack of sample automation, limited range of image magnification and the lack of appropriate laser excitation lines. In some cases, investigators have been unable to take advantage of this technology for certain applications such as FRET because the necessary laser excitation or channel separation is not available. With the introduction of the ImagestreamX, these limitations have been addressed and will allow our investigators to move projects forward more efficiently and in a cost effective manner. In addition, several investigators will be able to initiate studies that were not previously feasible with the Imagestream 100.